1. Field of the Invention
The present invention relates to a light source unit having a light source and an electric component for supplying current to the light source. Further, the present invention relates to a lighting apparatus and a notice bearing apparatus utilizing the light source unit.
2. Description of Related Art
Conventionally, several methods are known to illuminate a notice bearing apparatus, such as a signboard or an indicator, with utilizing a light source in order to be visible even in the night. For example, it is known about a method (exteriorly illuminating method) that mounts a color film or a color poster on a plane and illuminates from the front with a light source, a method (interiorly illuminating method) that sets a light source behind a transparent material (such as a plastic plate) and illuminates from the back, a method (self illuminating method) that machines a light source (such as a fluorescent lamp and a neon tube lamp) to be a desired shape (such as a character and a figure to be visible), and the like.
The light source such as the fluorescent lamp and the neon tube lamp has a limited short life, which causes to require frequent maintenances for replacing the light source. In the case that such the light source is set at a higher place (e.g., an outside signboard), a user happens to take larger burden. Thus, there is a need for reducing the maintenance frequency. Since a light emitting diode (LED) has been recently improved to emit a high intensity light, the conventional light source such as the fluorescent lamp and the neon tube lamp is exchanged to such the LED that has lower power consumption, longer life and the like.
In the case of the interiorly illuminating method and the self illuminating method that require arranging light sources based on the shape of a character or a figure to be visible and making the light sources emit light in order to display the character or the figure, the design flexibility is especially required for arranging the light sources at desired positions. The LED can satisfy such the requirement since the LED is a small light source and it is possible to manufacture an emitting light surface of LED in a desired shape.
In the case that such the LED is utilized as the light source and then respective LEDs must be arranged according to the shape of the character or the figure, a larger burden is required for fixing works and cable installing works of many LEDs. Thus, a light source unit is utilized, into which many LEDs are packaged without compromising the design flexibility for arranging the LEDs.
For example, it is known to connect a plurality of such the light source units and to supply constant current to the plurality of connected light source units from a constant current supplying circuit provided with a power supply section. Such the configuration has a problem causing variations in brightness due to variations in current supplied to the LEDs, because of variations in the voltage-current characteristic among manufactured LEDs, changes in the forward voltage based on heat, changes in the voltage reduction at the cable and the like. Thus, it is proposed to utilize light source units, each of which interiorly possesses the constant current supplying circuit (for example, Patent Document 1).
The light source unit proposed by the Patent Document 1 is configured to have a casing whose top face is opened, to include a plurality of LEDs and a circuit board mounting a transformer, a rectification circuit, a constant voltage supplying circuit and a constant current supplying circuit, and to contain the plurality of LEDs and the circuit board within the casing. This configuration can supply constant current to LEDs in each light source unit, and can implement preventing the variations in brightness with properly keeping the design flexibility for arranging the LEDs.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-310090